Cell structure - microscopes/using a microscope

Question 1

Define resolution

Answer 1

The ability to view detail.
The minimum distance between 2 points where they can still be seen.

Question 2

Define magnification

Answer 2

How many times bigger an image is than real life
e.g. x100

Question 3

What is the magnification equation?

Answer 3

magnification= image size / actual size

Question 4

Optical microscopes:
1)how does it work?
2)magnification
3)resolution
4)advantage
5)disadvantage

Answer 4

1)uses a beam of light and focuses at the object
2)up to x1500 (maybe x2000)
3)200nm
4)relatively cheap, easy to use, portable
5)has low magnification compared to others

Question 5

Scanning electron microscope:
1)how does it work?
2)magnification
3)resolution
4)advantage
5)disadvantage

Answer 5

1)electrons don’t pass through specimen but cause secondary electrons to ‘bounce off’ the specimens surface - focused on a screen
2)x15 - x200,000
3)1-20nm
4)high magnification, can add colour to black and white image
5)large, expensive, needs lots of skill, specimen need to be dead

Question 6

Laser scanning microscope:
1)how does it work?
2)magnification
3)resolution
4)advantage
5)disadvantage

Answer 6

1)uses a laser light to scan an object point by point and assemble on a computer
2)x100 - x17,000
3)180nm - 500nm
4)they have high contrasts
5)expensive

Question 7

Transmission electron microscope:
1)how does it work?
2)magnification
3)resolution
4)advantage
5)disadvantage

Answer 7

1)beam of electrons passes through the specimen - strained with metal salts
2)up to x2million (new ones up to x50million)
3)0.2nm
4)high magnification
5)large, expensive, needs lots of skill, specimen need to be dead

Question 8

what is a graticule and stage graticule?

Answer 8

microscope eyepiece fitted with a graticule - it’s transparent with a small ruler etched on it
The scale of the eyepiece graticule is arbitrary (represents different lengths at different) - the eyepiece scale has to be calibrated (worked out)
A stage graticule is used only to calibrate the eyepiece graticule

Question 9

how to use a stage graticule to calibrate the eyepiece graticule?

Answer 9

Stage graticule = microscopic ruler on a special slide
e.g.ruler is 1mm long and divided into 100 divisions - each division is 0.01mm or 10 micrometers
1)insert an eyepiece graticule into x10 eyepiece - ruler has total of 100 division
2)bring it to focus using x4 (total magnification = x40)
3)check value of 1 eyepiece division
4)e.g.stage graticule is 1mm (1000 micrometer) = 40 eyepiece divisions)
5)1000/40 micrometers = 25 micrometers
6)then use x10 objective lens (total magnification = x100)
1000/100 micrometers = 10 micrometers

Question 10

what is differential staining?

Answer 10

stains are coloured chemicals that bind to molecules in/on the specimen
-but some stains bind to specific cell structures, staining each structure differently so the structures can be easily identified within a single preparation

Question 11

what to do for scientific drawing from a microscope?
1)low power plan
2)high power plan

Answer 11

1)-use title
-add magnification used
-indicate scale (how much bigger it is from the size of image)
-it is of the specimen to show where different tissues are
-use unbroken line
-label structural features
-don’t draw individual cells
2)-use title
-add magnification
-indicate a portion of the tissue you will draw
-bigger objective lens used
-make separate drawing of 2 or 3 cells form each region
-don’t shade
-label structure features